The present invention relates to a system for preventing frost from accumulating on a vehicle window such as a windshield.
In order to prevent frost from accumulating on a windshield of a vehicle, Japanese Patent Laid Open No. 58-174046 discloses an electric circuit where an ambient temperature sensor, switch responsive to the output of the sensor, and a time relay are provided between a battery and a wiper motor. When the ambient temperature decreases below a predetermined temperature while the vehicle is parked, the sensor, switch and the time relay are actuated in turn so as to intermittently drive the wiper motor. Thus, wipers wipe away the frost on the windshield. However, the wipers only clear a certain area of the windshield so that a field of view is limited to a predetermined range.
U.S. Pat. No. 4,084,126 discloses a control system. In accordance with the system, a heating element of transparent metal film is embedded in a laminated windshield. When there is an ice accumulation on the windshield, a large amount of current flows from an alternator through the heating element at the start of the vehicle so that the windshield is de-iced in two to four minutes. However, in order to obtain a necessary current, a high voltage must be applied to the heating element. Therefore, means such as a DC/AC converter for converting direct current into alternating current is necessary, which causes the cost of the device to rise. In addition, a large amount of power more than 1500 watt is consumed for de-icing at a time. Accordingly, an alternator and battery having large capacities must be provided.